1. Technical Field
The present invention relates to a unidirectional condenser microphone of which the directionality is selectable in accordance with the usage and a directionality varying member for the unidirectional condenser microphone. The directionality varying member can vary the directionality of the unidirectional condenser microphone.
2. Background Art
A condenser microphone may be unidirectional, bidirectional, or nondirectional. Unidirectional condenser microphones may have a sub-cardioid directional pattern that is sensitive over a wide range or a hyper-cardioid directional pattern that is sensitive over a narrow range. These unidirectional condenser microphones are appropriately selected in accordance with the usage.
For example, a unidirectional condenser microphone having a normal cardioid pattern may be selected for picking up the voice of a single speaker with a single microphone. A unidirectional condenser microphone having a sub-cardioid pattern is suitable for picking up the voices of multiple speakers with a single microphone. A unidirectional condenser microphone having a hyper-cardioid pattern is suitable for picking up the voice of a specified speaker while preventing the pickup of the voices of other speakers and surrounding noise.
Usually, the directional pattern of a unidirectional condenser microphone is established during a production process. Thus, the selection of a unidirectional condenser microphone having the most appropriate directional pattern for the usage and usage environment of the microphone requires the preparation of multiple unidirectional condenser microphones having different directional patterns.
The directional characteristics of a unidirectional condenser microphone depend on the acoustic resistance and the distance between the front acoustic terminal and the rear acoustic terminal. The acoustic resistance can be adjusted by varying the thickness of the material of the acoustic resistor. For example, compression of the material causes an increase in the acoustic resistance. An increase in the acoustic resistance near the rear acoustic terminal leads to a sub-cardioid pattern, whereas a decrease in the acoustic resistance due to low compression of the material of the acoustic resistor leads to a cardioid pattern. A microphone is known which includes an acoustic resistor having a thickness variable with a screw to readily adjust the directional pattern of the microphone (for example, refer to Japanese Unexamined Patent Application Publication No. 2010-288047).
A unidirectional condenser microphone having a hyper-cardioid pattern is different from a unidirectional condenser microphone having a cardioid pattern in that the unidirectional condenser microphone has a larger distance between the front acoustic terminal and the rear acoustic terminal. A structure is known which has a cylindrical member (hereinafter referred to as “cap”) attached to the front surface of the microphone case in order to increase the distance between the front and rear acoustic terminals. The cap attached to the front surface of the microphone case causes the front acoustic terminal to be positioned more forward than usual, i.e., more forward than that of a microphone having a cardioid directional pattern. Such a cap is composed of a material other than that of the microphone and is detachable from the microphone. A microphone equipped with such a cap has a hyper-cardioid directional pattern, while a microphone with the cap removed has a cardioid directional pattern.